1. Field of the Invention
This invention pertains generally to nonwoven fibrous webs, and more particularly to processes for coloring such nonwoven webs.
2. Description of the Prior Art
It is often desired to provide a nonwoven wiper which has greater thickness, bulk and absorbency than paper towels which are formed by the standard wet laying processes. To achieve greater bulk and absorbency, fibrous material may be air-layed in a substantially dry state to form a web, with the fibers of the web then being bonded together by a binder material, such as a polymeric latex which is applied in a liquid state to the web and is dried and cured with cross-linking of the polymer molecules. Typically, such webs are colored by applying dye solutions to the formed web and allowing the dyes to thoroughly soak into the web to color all of the fibers of the web.
In certain air-layed web forming processes, the purified pulp fibers are first formed into a heavy web which is subsequently dried to relatively low moisture content. The dried web is then run through a defiberizer such as a hammermill to reproduce the separated individual fibers, which are then blown down onto a moving fine screen on which the air-layed web is formed. The formed web is then pressed and the binding liquid is applied thereto to provide the necessary binding of the fibers. Such webs have also been colored by the application of dye solutions, either to the formed web, or to the initial pulp web before it is fiberized.
While dyes have been extensively used to provide the coloring in nonwoven webs, the dyes themselves present troublesome problems where the nonwoven webs are to be used in a wet environment, such as with household wipers. These wipers must maintain their structural integrity over a period of use in a wet environment, and must not be subject to bleeding of the coloring material or to rubbing off of the color onto the surface being cleaned. Because the dyes used in papermaking ordinarily must be nontoxic and are preferably relatively inexpensive to use in the large scales encountered in papermaking, the dyes actually utilized are water soluble and even after fixing do not have satisfactory bleed and rub resistance.